1. Field of the Invention
The present invention relates to a head unit, an ink-jet cartridge and a liquid ejection apparatus. Particularly, the invention relates to an ink-jet head unit, an ink-jet cartridge and an ink-jet printing apparatus for performing printing with ejecting an ink and a printing ability improving liquid (hereinafter simply referred to as “processing liquid”) which makes a coloring material in the ink insoluble or coagulates the coloring material.
The present invention is applicable for all of devices or apparatuses which employ a paper, a cloth, a leather, a non-woven fabric, an OHP sheet and so forth, and even a metal and so forth as media (hereinafter simply referred to as “printing medium”) receiving inks and the printing ability improving liquid. Concretely, the present invention is applicable for an office machine, such as a printer, a copy machine and a facsimile machine, an industrial production machine and so forth.
2. Description of the Related Art
Conventionally, an ink-jet system has been widely used in a printer, a copy machine and so forth due to its advantages of low noise, low running cost, compactness of the apparatus, and ease of color printing.
However, in a printing apparatus employing such ink-jet system, if a printing medium called plain paper is used, bleeding occurs on the printing medium upon deposition of water or so forth due to insufficiency of resistance of a printed image to water. Also, upon color printing on the plain paper, it has not been possible to achieve both of a high density image without causing feathering and an image without bleeding between colors. Therefore, it may be possible that a color image with sufficient fastness property or satisfactorily high print quality cannot be obtained.
As a solution for the problem set forth above, an ink providing water resistance for a coloring material contained in the ink has been recently put into practice. However, the water resistance of the ink is still insufficient. Also, such water resistive ink is difficult to dissolve in water after once dried in principle, and it has a tendency to easily cause plugging in ejection openings or so forth in an ink-jet printing head. On the other hand, a construction of the apparatus required for preventing plugging of the ejection openings becomes complicated.
Also, there have been various proposals for improving fastness property of the printed products.
For example, Japanese Patent Application Laid Open No. 24486/1978 proposes subjecting a printed product to a post treatment for converting a dye into a lake for fixing in order to enhance color fastness against wetness of the printed product.
On the other hand, Japanese Patent Application Laid-open No. 43733/1979 discloses a method for performing printing with employing a substance containing two or more components which increases a layer forming ability by contacting with each other under room temperature or heated condition, in the ink-jet system. In this method, a printed product having a layer firmly fixed on the printing medium can be obtained by contacting the components on the printing medium.
Also, Japanese Patent Application Laid-open No. 150396/1980 discloses a method for, after printing, applying an agent for making the dye water resistant to a water based ink so as to react with the dye in the ink to form a lake.
Furthermore, Japanese Patent Application Laid open No. 128862/1983 discloses an ink-jet printing apparatus for performing printing by preliminarily recognizing positions on which dots are formed and by providing a printing ink and a processing ink on the recognized positions in overlaying manner. Here, enhancement of water resistance of the printing product has been attempted by ejecting the processing ink in advance of ejection of the printing ink, conversely by ejecting the processing ink over the preliminarily ejected printing ink, or by ejecting the printing ink after overlaying the printing ink on the preliminarily ejected processing ink.
On the other hand, it has been well known that the ink-jet printing system encounters the following problem.
At first, in the ink-jet system, a fine ink droplet which is much smaller than an ink droplet to be ejected may be generated associated with ejection of the ink droplet. Further, a fine liquid droplet may be generated when the ink droplet ejected rebounds on the printing medium. These liquid droplets will occasionally form a mist of fine liquid droplets, and such mist may deposit on a surface of an ink-jet head on which an ejection opening is formed. When a large amount of the mist is deposited around the ejection opening, or when paper dust or other foreign matter adheres on the mist deposited around the ejection openings, ink ejection can be affected, causing variation in the ejecting direction of the ink droplet (hereinafter also simply referred to as “deflection”), failure of ejection of the ink droplet and so forth.
Secondly, in the ink-jet head, while ejection is not performed, particularly when a non-ejection state is maintained for a long period, viscosity of the ink in the ejection openings can increase and the ink can solidify. Also in this case, deflection, ejection failure or so forth can be caused.
It has been known that the following construction is provided in the ink-jet printing system for avoiding the foregoing inconvenience.
Concerning the first problem, in order to prevent the mist from depositing on non-specified portions of the ink-jet head, improvement of the head per se or introduction of air flow generated by a blower fan into a gap between the head and the printing medium are attempted, for example. By the effect of the former, reduction of the amount of the mist to be generated can be observed. However, in the latter case, since the flying direction of the ejected ink droplet can be disturbed by the air flow, the air flow has to be relatively weak and then the weakness of the air flow can cause the mist deposit prevention to be insufficient.
Furthermore, it is also known to deposit the ink mist to a predetermined region by applying an electric field to the ink mist per se. The fine ink droplets forming the ink mist may not be polarized at specific polarity upon separation into the fine droplets, and also, a non-polarized ink droplet may be generated. As a result, control of the ink mist deposit region by the electric field cannot be performed effectively.
In addition, as a means for cleaning and removing the ink, paper dust or so forth once deposited on an ejection opening forming surface of the head due to generation of the ink mist, it has been generally known to wipe the ejection opening forming surface, using a blade made of an elastic material, such as rubber or so forth.
Concerning the second problem, it has been known to cover the ejection opening forming surface with a cap while not printing, so as to prevent the ink from evaporating and drying, so that increasing of viscosity and solidification of the ink in the ejection opening of the ink-jet head can be prevented. Also, if the ejection failure is caused by increasing of viscosity or solidifying of the ink, or if foreign-matter that cannot be removed by the blade which is set out with respect to the first problem, resides on the ejection opening forming surface, normal ejection is recovered by suctioning the ink of increased viscosity in the ejection opening or the ink deposited on the ejection opening forming surface with a suction pump connected to the cap, so as to expel the ink of increased viscosity or so forth.
Furthermore, in printing operation of an on-demand type ink-jet printing system, while it depends on the printing data, not all of a plurality of ejection openings provided on the head are used for printing in most cases. Therefore, some ejection openings may not be used for a predetermined period or longer. Also, in the case where an ink-jet head is provided for each color, such as in a color printing apparatus, depending on printing color, printing data may be not transferred (ejection of the ink is not performed), and all of ejection openings of the head for ejecting the certain color of ink may be held in non-use. Therefore, the printing operation may be continuously performed under the condition where non-use ejection openings are present. Also in such case, the ink is evaporated and drying of the ink in the ejection opening or on the ejection opening forming surface of the head is promoted where the ink ejection is not performed to result in lowering of ejection performance and thereby cause lowering of printed image quality.
For such problem, it has been further known to perform a preliminary ejection operation in addition to the suction recovery as set forth above or separately therefrom. In the preliminary ejection operation, ink ejection is performed at a predetermined position irrespective of the printing data at a given interval so as to expel the ink in the ejection opening and introduce fresh ink to maintain an appropriate condition of the head for ejection. The preliminary ejection is performed by ejecting the ink into the cap of the recovery unit or toward a preparatory ejection receptacle member provided separately, for example, so that scattering of the ejected ink to the printing medium or the inside of the apparatus causing contamination, can be successfully avoided.
However, in the ink-jet printing apparatus, it is possible that the conventionally known problem of water resistance of the printing product and the problem associated with ejection failure cannot be easily solved simultaneously.
More specifically, when the processing liquid which makes the ink insoluble is used for water resistance and enhancement of the image quality, while water resistance and the image quality and so forth can be improved, the ink in mist state, which becomes insoluble, is deposited at the ejection opening portions and the vicinity thereof or the ejection opening forming surface, and such deposits become difficult to remove by wiping or preliminary ejection set forth above to result in more a critical problem, such as relatively serious ejection failure.
Deposition of the insoluble ink is caused mainly by the following two phenomena. The first phenomenon is the case where the ink droplet and the processing liquid ejected from the ink-jet heads rebound on the printing medium and deposit in the ink-jet head in admixed form. Particularly, the first phenomenon arises in the case where the ink droplet is ejected to a portion to which the processing liquid is already ejected and where the processing liquid and the ink droplet rebound and deposit as an already reacted insoluble substance. The second phenomenon is that the printed portion of the paper is in contact with the ejection opening portion of the ink-jet head, and can form the insoluble substance upon occurrence of jamming of the paper or so forth as the printing medium or occurrence of feeding of a plurality of papers in a stacked manner.
On the other hand, the inventors of the present application have studied the ink mist generated in the conventional apparatus and determined that most of the conventionally recognized ink mists have droplets of relatively large volume so as to have relatively high motion speed. More specifically, the conventionally well known ink mist is moved by its own motion energy along a direction which is determined when the motion energy is given to the ink mist to certainly reach the head, the printing medium or functional portion within the apparatus so as to cause the deposition phenomena set forth above. Accordingly, in order to prevent deposition phenomena of the ink mist, certain means, which can oppose the motion energy of the ink mist, becomes necessary.
On the other hand, providing such opposing means in the printing apparatus results in affecting the ejected ink droplets for formation of the image in most cases, and can increase the cost. As a result of this, practical problems are encountered.
The inventors have re-studied conditions under which ink mist is generated, and have conducted extensive research from a viewpoint which has not been considered conventionally to reach a novel invention.
Particularly in the case where the processing liquid is used together with the ink, since the later ejected liquid droplet collides with the liquid state droplet formed at prior effected ejection, on the printing medium, most of the mist generated is caused by rebounding. In this case, the rebounding mist has large motion energy to deposit on the non-specified positions. The inventors have studied this case to reach the present invention.